For those still doubting the power of the roundabout

The MythBusters decided to test the 'myth' that European-style roundabouts were more efficient - allowing a higher throughput - than the 4-way stop intersection that dominates in North-America. Here's the test segment:

Other benefits of roundabouts

Please note that what they are testing for is the number of cars that can cross the intersection in a certain period of time. That one thing, but there are others; for example, roundabouts also have fuel-efficiency benefits because you often don't have to completely stop the vehicle, losing momentum and making the engine work harder to re-accelerate. They've also been shown to be safer (including for pedestrians).

I can say that, from personal experience, that seems true. I don't live in Europe, so there aren't that many roundabouts around, but my city built three of them close to where I live and, after people got used to them, they seem to be much faster and safer (except when a driver who's not familiar with the concept goes through for the first time).